The present invention relates to a method and a device for performing perforating operations in a well and notably a well destined for oil production.
According to a method which is well-known by drilling specialists, bringing an oil well into production is achieved by taking down into a cemented well a tubing of a section smaller than that of the well. A perforating tool such as a gun containing one or several explosive charges is fastened at its base through removable connecting means. The tubing is equipped towards its lower part with a preventer stack such as a packer the dilatation of which, controlled from a surface installation, allows to close the annular space between the wall of the well and the tubing and to immobilize the latter when the gun has reached the required depth. The triggering of the gun is carried out by taking down into the tubing a percussion bar adapted for striking a detonator at the top of the gun, through the opening of a valve allowing to apply a hydraulic overpressure which is imposed in the tubing, or else through an electric igniting by taking down a female electric connector to a complementary connector disposed in the upper part of the gun. When the well begins to produce, owing to the performed perforatings, the total lower part of the tubing below the packer is removed in order to clear the passageway to the surface and this part falls to the well bottom. Specialists often call these perforating systems TCP (tubing conveyed perforating) systems.
Different systems of this type have been described, among other examples, in U.S. Pat. Nos. 4,633,945 or 4,756,371, or in European Patent Application 288,239.
In such a perforating system, the distance between, the packer and the gun is often several meters (e.g., more than 20 meters) owing to stiff tubular sections interposed between both of them. It is thus obligatory to drill an additional well portion or "rathole" much beyond the depth where the perforatings will take place, so that the perforating system can fall down into this portion and the lower end of the tubing is cleared. Moreover, if several perforatings must be performed in one area of the well after the blocking of the packer, a perforating device with several stages spaced out from one another by tube sections must be used. The spacing must be selected in such a way that the perforatings occur at the wanted depths. This complicates the operations for mounting the device at the tubing bottom. Besides, owing to the greater length of the perforating device, the additional well length to be drilled in order to allow the gun to fall after use is greater.
U.S. Pat. No. 4,593,195 describes a device for bringing an intervention tool (such as a measuring sonde or a perforating gun) to the bottom of a well bore comprising a tubing fitted towards its lower end with an expansible packer, a support frame for the tool, disposed near the lower end of the tubing, a flexible linking element comprising an electric cable for linking the tool to its support frame and remote control means comprising a cable equipped with an electric connector that can be taken down along the tubing until it plugs into an additional connector carried by the support frame, in order to transmit electric control signals and/or tensile strains to provide the displacing of the tool.